1. Field of the Invention
This invention relates to a key switch which is used for a well-known key board for a computer or the like.
2. Description of Related Art
In general, a conventional key switch is so designed that a key stem which is provided so as to be vertically projected from the back face (surface) of a key top is upwardly and downwardly slidably inserted into a key holder portion formed on a holder plate. With the key switch thus constructed, if the key stem has a relatively-large portion to be slidably guided by the key holder portion, a key-operating performance would be more improved. However, in this case the requirement to thin the key board (reduce the thickness of the key board) cannot be satisfied. On the other hand, if the portion of the key stem to be slidably guided is designed to be of a small size (to be thinner) in order to satisfy the requirement to thin the key board, the key-operating performance declines due to "tanglement (friction)" occurring between the key stem and the key holder portion.
In order to solve the above problems of the conventional key switch, as disclosed in the Japanese Patent Application No. 3-330160 (corresponding to U.S. Pat. Nos. 5,280,147 and 5,278,372, the inventor of this application proposed a key switch in which the thinning of the key board was achieved by removing the key stem and the key holder portion at the same time the key-operating performance was improved.
The construction of the key switch as described above will be described with reference to FIGS. 14 to 16.
As shown in FIG. 14, the key switch comprises a key top 101, a guide support member 106 and a base portion 150. The key top 101 is formed of a resin and comprises two pairs of engaging portions 102 and 103, engaging holes 104 formed in the engaging portions 102, and engaging grooves 105 formed in the engaging portions 103.
The base portion 150 is designed in a three-layered structure and has a holder plate 125, a flexible circuit board 130 and a switch support plate 132. On the holder plate 125 are provided two pairs of engaging portions 126 and 127, engaging grooves 128 formed in the engaging portions 126, and engaging holes 129 formed in the engaging portions 127 for each key top 101. On the flexible circuit board 130 is provided a switch electrode (not shown) for each key top 101. Further, a rubber spring 131, containing a movable electrode, is provided so as to cover each of the switch electrodes. The switch support plate 132 has a degree of rigidity, and it is used to support the holder plate 125 and the flexible circuit board 130.
The guide support member 106 provided between the key top 101 and the base portion 150 is formed of two resin hinge members 107 and 108. As shown in FIG. 15, the first hinge member 107 comprises a base portion 109 and two base end portions 110 and 111 which are formed at both ends of the base portion 109 so as to be integral with the base portion 109. A shaft 112 is formed projectingly from the one side surface of a central portion of the base portion 109 and is supported while being inserted into a shaft hole 120 which is formed in the second hinge member 108. Further, the base portion 110 is provided with engaging pins 113 and 114 which project from the side surfaces of both end projecting portions 110A of the base portion 110. The engaging pins 113 and 114 are rotatably inserted into the engaging holes 104 formed in the engaging portions 102 of the key top 101. Further, the base end portion 111 is designed to be substantially U-shaped in plan view. Engaging pins 115 and 116 are provided projectingly from the side surfaces of both end projecting portions 111A of the U-shaped base end portion 111. The engaging pins 115 and 116 are slidably engaged with the engaging grooves 128 of the engaging portions 126 formed in the holder plate 125.
As shown in FIG. 16, the second hinge member 108 comprises a base portion 117 and two base end portions 118 and 119, which are formed at both ends of the base portion 117 so as to be integral with the base portion 117. A shaft hole 120 is formed at the center portion of the base portion 117. The shaft 112 of the hinge member 107, as described above, is inserted into the shaft hole 120. The base end portion 118 is designed to be substantially U-shaped in plan view. Engaging pins 121 and 122 are provided projectingly from both end projecting portions 118A of the U-shaped base end portion 118. The engaging pins 121 and 122 are rotatably inserted into the engaging holes 129 of the engaging portions 127 formed in the holder plate 125. Further, engaging pins 123 and 124 are provided projectingly from both end projecting portions 119A of the base end portion 119. The engaging pins 123 and 124 are slidably engaged with the engaging grooves 105 formed in the engaging portions 103 of the key top 101 as described above.
The guide support member 106 is constructed by inserting the shaft 112 formed in the base portion 109 of the first hinge member 107 into the shaft hole 120 formed in the base portion 117 of the second hinge member 108. Both of the hinge members 107 and 108 are mutually rotatable around a shaft support portion 106A comprising the shaft 112 and the shaft hole 120. Accordingly, the key top 101 is linked to the base portion 150 so as to be vertically movable. In addition, since the shaft support portion 106A is ordinarily disposed at the upper side of the rubber spring 131, the rubber spring 131 is buckled through the shaft support portion 106A of both hinge members 107 and 108 by pushing down the key top 101. Accordingly, the key switch thus constructed is so designed that the switching operation thereof is executed by short-circuiting the switch electrode using the movable electrode.
However, the conventional key switch as described above has a problem in that the assembly of the holder plate 125 and the guide support member 106 comprising the two hinge members 107,108 and the assembly of the guide support member 106 and the key top 101 cannot be simply and easily performed.
That is, in the case where the key switch as described above is assembled by a worker, the key switch must be assembled in accordance with the following procedure. First, the worker needs to assemble the first and second hinge members 107 and 108 so as to be intersected with each other, thereby constituting the guide support member 106. Subsequently, the worker press-fits both of the engaging pins 121 and 122 of the base end portion 118 of the second hinge member 108 into the engaging holes 129 of the engaging portions 127 of the holder plate 125. At this time, the press-fitting of the engaging pins 121 and 122 into the engaging holes 129 is carried out using the mutual resin elasticity of the end projecting portions 118A and the engaging pins 121 and 122. However, it is difficult for the worker to position each of the engaging pins 121 and 122 to the engaging holes 129. Therefore, the press-fitting work is carried out under a very instable condition and is very cumbersome.
In addition, in the case where the worker press-fits the engaging pins 115 and 116 of the base end portion 111 of the first hinge member 107 into the engaging grooves 128 of the engaging portions 126, the press-fitting work is also carried out using the mutual resin elasticity of the end projecting portions 111A and the engaging pins 115 and 116, so that this working is also cumbersome like the above press-fitting work.
As described above, the assembly of each hinge member 107, 108 with each engaging portion 126, 127 of the holder plate 125 is finished. Thereafter, each of the engaging pins 113 and 114 is press-fitted into the engaging holes 104 of the engaging portions 102 and each of the engaging pins 115 and 116 is press-fitted into engaging grooves 105. These press-fittings are also carried out using the mutual resin elasticity of the engaging pins 113,114,123,124 and the engaging portions 102,103. Thus these assembly operations are also cumbersome like the previously described assembly.
As described above, according to the key switch as disclosed in the specification and the drawings of the Japanese Patent Application No. 3-330160, the thinning of the key switch is more achievable and the key-operating performance thereof can be excellently improved as compared with the key board of the conventional key switch. However, for this key switch, the assembly of the hinge members 107,108 and the holder plate 125 and the key top 101 is carried out using the resin elasticity, and each of the engaging pins 113 through 116 and 121 through 124 is required to be fitted to the appropriate engaging hole 104,129 or engaging groove 105,128 while being positioned to the inside of that engaging hole or groove. Therefore, the complicated press-fitting work must be carried out for the entire assembly of the key switch.